This section provides background information related to the present disclosure which is not necessarily prior art.
Hybrid vehicles may be propelled by a powertrain including an internal combustion engine and one or more electric motors. During operation, drive torque may be supplied by the engine and/or the electric motors. Some hybrid engine systems stop the engine when the vehicle is brought to a stop and restart the engine when the vehicle begins to move again. One or more of the electric motors may supply the torque used to crank and thereby restart the engine.
The torque required to start the engine is related to engine cranking compression. Delaying the closing of engine intake valves may reduce cranking compression during the compression stroke. However, delaying the closing of the inlet valves may reduce engine torque over the operating speed range of the engine, requiring larger engine displacement to compensate for the reduced engine torque output.